1. Field of the Invention
This invention relates generally to the field of information security, and more particularly to an enrollment process for devices capable of storing and releasing personal identity credentials based on authentication of a human fingerprint.
2. Necessity of the Invention
Devices and applications that use biometric authentication are increasing in popularity and frequency of use in applications where information security and privacy is critical. The success rates of devices that use biometrics as a form of authorization are dependent on the accuracy of the process by which information is associated with the biometric; for example, it must not be possible for John Doe to intercept Jane Doe's enrollment process and enroll Jane Doe's credentials into a device with his fingerprint. A generalized enrollment process includes capturing a biometric sample, ensuring the legitimacy of the sample and the individual providing the sample, storing the biometric sample in the appropriate location in the device, and enabling access rights to the enrolled individual. If this enrollment process is performed incorrectly or ineffectively then the process of biometric authentication and the implicit guarantee of enhanced security are easily defeated.
A variety of portable electronic devices with biometric authentication are available to consumers. These include Hewlett Packard's iPAQ Pocket PC h5450, 3M-AiT's VeriMe, Privaris' BPID™ Security Device, and Sony's FIU-900 Puppy®. Each device is capable of storing fingerprints and performing on-board matching. Several of these products are configurable to allow use of cryptographic keys after proof of biometric identification. As discussed in the following section, ownership of cryptographic keys is typically used as a form of remote identification when individuals are communicating digitally. It is imperative, then, that the fingerprint is definitively linked to an individual, so that the cryptographic keys cannot be misused.
Furthermore, because the enrollment process must necessarily be stringent, and likely time-consuming, it is desirable to have a simple method of archiving and restoring enrolled credentials and fingerprints. Clearly the method must be inherently secure, because the entire enrollment process could be overridden by a compromise of the backup process.
3. Description of the Related Art
Public Key Infrastructure
The public key infrastructure (PKI) and digital certificates are very common and, when used correctly, can be used to guarantee a ‘cryptographic identity’ of an individual. The most common form of the PKI uses the RSA algorithm, which is now freely available to the public.
To use the PKI, an individual—Alice—applies for a digital certificate from a trusted authority. After a substantive background investigatory process, the trusted authority decides that Alice is who she claims to be and decides to issue a digital certificate. The certificate includes a public key, one half of an asymmetric key pair, which is assigned only to Alice. She retains the other half of the key pair, the private key. Due to the fundamental principles of public key cryptography, anything encrypted by the Alice's private key can only be decrypted using her public key, and vice versa. Alice is free to distribute the digital certificate and the public key to whomever she wishes.
When another individual, Bob, wishes to send a message to Alice, he encrypts it with her public key. Alice receives the encrypted message and uses her private key to decrypt it. Because Alice is the unique owner of her public key, Bob knows that she possesses the unique and accompanying private key. Additionally, Bob sees that a trusted authority, which he knows performs substantive background checks, issued the digital certificate issued to Alice. He is assured that the only person who can read the message is truly Alice. This assures one-way security.
However, Alice cannot be sure that Bob sent her the message, because her public key is freely accessible. To combat this problem, Bob also requests and receives a digital certificate from a trusted authority. Bob writes his message and then creates a digital signature for the message. He first creates a hash of the message; this process creates a fixed-length string that is unique to the message but cannot be used to deduce the message. He then encrypts this hash using his private key and appends the encrypted hash to his message. The message and encrypted hash are now encrypted with Alice's public key, and transmitted to her.
Alice first decrypts the message with her private key. She can now read the message, as described above. However, she also has the encrypted hash, which she can use to verify that Bob sent the message. She uses Bob's public key to decrypt the digital signature and obtain the hash. Alice then hashes the received message herself, using the same hash algorithm as Bob. If she obtains the same hash value as the one transmitted by Bob, she is assured that the message has not changed, and that he did actually send the message.
Enrollment Processes
3M-AiT's VeriMe stores a biometric template and a cryptographic private key for one user. When the user wishes to use the cryptographic private key, he or she must supply the correct biometric template. According to the VeriMe fact sheet, the private key is generated at the time of “secure registration” of the fingerprint. However, the fact sheet does not describe the secure registration or what it entails; it also does not discuss a secure backup and recovery process.
Biometric Associates (BAI) produces a fingerprint sensor that can be embedded into a smartcard. The smartcard can then be used to perform local biometric authentication, like the devices described above. According to BAI's website, the cards can enroll up to eight users with the use of a BAI Enrollment Station. The Enrollment Station provides external equipment necessary to instruct the smartcard to start enrolling fingerprints and personal credentials. However, the published information does not describe a secure cryptographic process for accomplishing this. It also does not describe secure backup and recovery processes.